Die casting is the process developed for manufacturing accurately dimensioned, sharply defined, smooth-surfaced metal parts by forcing liquid metals and alloys, under pressure, into metal dies, where solidification takes place. In simple form it is: "B.T.U.'s in, conform to the configuration of the part desired, B.T.U's out". Optimum casting quality requires minimizing porosity, segregation, shrinkage and inclusions, plus good surface finish.
There are on the market today several types of instruments with which to monitor the die casting process. Examples of these are die temperature controllers, metal temperature controllers, shot speed controllers and measurement devices. All of these units, however, require an individual with technical knowledge to interpret the information provided by these instruments. The technician must then make the proper adjustments to correct any problem that may exist.
These variables in the die cast process interact with each other in several ways, making proper assessment of these variables on an individual basis very difficult. Rather, they must be examined simultaneously, because changes in any or all of the variables could affect the quality of the die cast product. Thus, the human approach is undesirable where rapid solutions are required. The fastest, most accurate approach, is to analyze the data collected from the die cast machine on a digital computer, and feed back the adjustments necessary through a P.C. controller.
Prior control systems have included a servo controlled shot cylinder for a die-casting machine including a quick response linear displacement transducer for producing a signal of shot ram velocity. Programmable means are provided for comparing the actual shot ram velocity with a command velocity signal and means operative in response to the comparison cycle a hydraulic servo valve to on-off states thereby to produce modulation of flow from a hydraulic shot valve to compensate for changes in velocity produced by operating variances in fluid mechanics of the system.
An object of the present invention is to improve a system of the preceding type by the provision of an additional micro-computer and associated sensing means for monitoring die casting variables including metal temperature, and die temperature and wherein these variables are compared with pre-set values to adjust the shot cylinder.
A further object of the present invention is to provide an improved method of die-casting including measuring the material temperature in the outlet region of an injection chamber just prior to a pressure casting shot; comparing this temperature against a pre-set value that was previously established by the operator during set-up; and, if the metal temperature is below the preset value, increasing the shot speed accordingly and if the temperature is higher than the preset value, reducing the shot speed and if the material temperature is at predetermined out-of-limits so that the shot speed cannot be compensated, terminating the machine cycle.
A further object is to provide an improved method as set forth in the preceding object wherein die temperature is measured just prior to shot and during a dwell period and shot speed adjustments are based on the die temperature, in the same manner as with the metal temperature; and, during the dwell period, when the die temperature drops to a preset limit, opening the die to open to eject the casting.
Yet another object is to provide an improved method as set forth in the two preceding objects including monitoring a shot cylinder position while the casting shot is moving forward, and triggering a fast shot when hot metal is detected at the die-casting gate and time controlling the length of fast shot based on a required cavity fill time; and if the shot plunger's cylinder position exceeds a preset value (based on metal volume), aborting the shot.
Another object of the present invention is to provide an improved control system for a die-casting machine including providing a programmable computer and sensing means for measuring the metal temperature at multiple points in the metal injection flow paths of the machine including sensing means for measuring the metal temperature at least in the outlet region of a cold chamber of a die-casting shot; the programmable computer instantaneously comparing the sensed metal temperature with a pre-set computer input value and either increasing or decreasing a shot speed command signal to adjust the shot speed of the machine.
Still another object is to provide an improved control system of the type set forth in the preceding object wherein second sensing means are provided to sense die temperature just prior to the die casting shot and during the dwell period and resultant signals of die temperature are instantaneously compared with pre-set values of desired die temperature to adjust the shot speed in accordance with die temperature in the same manner as with the first sensed metal temperature and to instantaneously compare the die temperature as it drops during the machine's dwell period with a pre-set dwell limit temperature to produce a signal to open the die and eject the die-casting at the completion of a casting cycle.
Another object of the present invention is to provide an improved control system for a die-casting machine as set forth in either of the precedingobjects by the provision of means for monitoring the shot plunger's cylinder position and means for sensing when hot metal is detected at the gate to the casting cavity and including a computer program that instantaneously compares the occurrence of the gate metal signal with a preset timed period value of fast shot length based upon the time required to fill the die cavity; the computer including means operative to abort the shot if the metal-at-gate condition is sensed when the shot plunger's cylinder position exceeds a pre-set value (based on metal volume).
These and other objects and features of the present invention will be apparent to those skilled in the art to which it relates from the following description made with reference to the accompanying drawings.
These and other objects and features of the present invention will be apparent to those skilled in the art to which it relates from the following description made with reference to the accompanying drawings.